1. Field of Invention
The present invention relates to a printed-wiring-board conveying method and a printed-wiring-board conveyor and particularly to the improvements of such a printed-wiring-board conveying method and a printed-wiring-board conveyor each of which employs a wound-on member, such as a belt, for conveying a printed wiring board.
2. Related Art Statement
There is known a printed-wiring-board (xe2x80x9cPWBxe2x80x9d) conveyor which includes an endless, annular conveyor belt, a plurality of pulleys on which the conveyor belt is wound, and a drive device which drives or rotates at least one of the pulleys. The conveyor belt includes a straightly and horizontally extending portion which directly supports a lower surface of a PWB. When one pulley is rotated by the drive device and accordingly the conveyor belt is moved, the PWB is conveyed by a frictional force produced between the PWB and the conveyor belt.
However, the above-indicated PWB conveyor has some problems. For example, the speed at which the PWB is conveyed has an upper limit, and accordingly it is difficult to improve the efficiency of conveying of PWBs. Though the PWB is conveyed by the frictional force produced between the PCB and the conveyor belt, as indicated above, the frictional force depends on the weight of the PWB and the coefficient of friction between the PWB and the conveyor belt. Therefore, the PWB cannot be conveyed at an acceleration greater than a maximum or upper-limit acceleration depending on gravitational acceleration.
In addition, since the above-indicated PWB conveyor conveys the PWB while supporting the lower surface thereof, many elements of the PWB conveyor are provided under the PWB, so that little free space is left under the PWB. Thus, it is not easy to provide another or other devices under the PWB. In addition, the PWB conveyor cannot help having a great vertical dimension. Thus, the conventional PWB conveyor suffers from a low degree of freedom.
The present invention provides a printed-wiring-board conveying method and a printed-wiring-board conveyor that have one or more of the following technical features that are described below in respective paragraphs given parenthesized sequential numbers (1) to (18). Any technical feature that includes another technical feature shall do so by referring, at the beginning, to the parenthesized sequential number given to the latter feature. Thus, two or more of the following technical features may be combined, if appropriate. Each technical feature may be accompanied by a supplemental explanation, as needed. However, the following technical features and the appropriate combinations thereof are just examples to which the present invention is by no means limited. In addition, in the case where one technical feature recites a plurality of items, it is not essentially required that all of those items be simultaneously employed. That is, it is possible to select and employ only a portion (one, two, . . . , but not all) of those items of that technical feature.
(1) According to a first feature of the present invention, there is provided a method of causing a wound-on member to contact a printed wiring board and conveying the printed wiring board by utilizing a frictional force produced between the wound-on member and the printed wiring board, the method comprising the steps of providing two conveying units each of which includes a wound-on member and two rotatable wheels on which the wound-on member is wound to have a straightly extending portion which straightly extends between the two rotatable wheels, such that the two conveying units are spaced from each other in a direction parallel to a printed wiring board, and such that the respective straightly extending portions of the two wound-on members of the two conveying units cooperate with each other to sandwich the printed wiring board in a direction substantially parallel to the printed wiring board, and conveying the printed wiring board by rotating the rotatable wheels of the two conveying units, and thereby moving the two wound-on members, while utilizing a frictional force produced between each of the two wound-on members and the printed wiring board. The printed wiring board may be one on which electric components (xe2x80x9cECsxe2x80x9d) have been mounted and electrically connected to electric circuits, or one on which no electric components have been mounted. At least one of the rotatable wheels may be driven by a drive device, and this rotatable wheel will be referred to as the xe2x80x9cdrive rotatable wheelxe2x80x9d. Since the printed wiring board (xe2x80x9cPWBxe2x80x9d) is conveyed while being sandwiched by the two conveying units in the direction substantially parallel to the upper and lower major surfaces of the PWB, the two conveying units can be provided on both sides of the PWB and accordingly a large space can be left under the PWB. In addition, the two conveying units can be easily constructed so as to be generally flat as seen in the direction parallel to the PWB. Moreover, in the case where the two wound-on members contact the PWB with a contact force greater than the weight of the PWB, the two wound-on members can move the PWB at an acceleration higher than a maximum acceleration that can be achieved depending on gravitational acceleration. The last advantage contributes to increasing the speed at which the PWB is conveyed and thereby improving the efficiency of conveying of PWBs. The present PWB conveying method may employ at least one of the second to eighteenth features (2) to (18) of the PWB conveyor, described below.
(2) According to a second feature of the present invention, there is provided a printed-wiring-board conveyor, comprising at least one wound-on member; at least two rotatable wheels on which the wound-on member is wound to have a straightly extending portion which straightly extends between the two rotatable wheels and which contacts a printed wiring board; a drive device which drives at least one of the two rotatable wheels and moves the wound-on member while utilizing a frictional force produced between the wound-on member and the printed wiring board; and a contact-force producing device which causes the straightly extending portion of the wound-on member and the printed wiring board to contact each other with a contact force greater than a weight of the printed wiring board. The wound-on member may be a belt such as a V-belt, a round belt, a flat belt, or a cog belt (i.e., a timing belt); a wire; or a chain. The rotatable wheels may be pulleys such as V-pulleys or flat pulleys; or sprockets, and can be selected corresponding to the sort of the wound-on member employed. The rotatable wheels may be ones which are rotatable about respective axis lines intersecting a reference plane parallel to the PWB, or about respective axis lines parallel to the reference plane. In the former case, the respective axis lines of the rotatable wheels may be perpendicular to the reference plane and, in this case, the wound-on member is circulated on a plane parallel to the reference plane; and in the latter case, the wound-on member is circulated on a plane perpendicular to the reference plane. However, depending upon the circumstances, the rotatable wheels may be rotated, as needed, about respective axis lines whose directions differ from each other, so that the wound-on member is circulated on a curved surface. The PWB may be conveyed in a horizontal direction, or in a direction inclined relative to a horizontal direction. The present PWB conveyor may employ two conveying units according to the third feature (3), at least three conveying units according to the fifteenth feature (15), or at least one conveying unit according to the seventeenth feature (17). In the third feature (3), the two conveying units convey the PWB while sandwiching the PWB in a direction substantially parallel to the above-indicated reference plane. In the fifteenth feature (15), two conveying units convey the PWB while sandwiching the PWB in a direction substantially parallel to the reference plane, and one conveying unit conveys the PWB while supporting the lower surface of the PWB. In the seventeenth feature (17), the conveying unit conveys the PWB while supporting the lower surface of the PWB. In each case, the contact-force producing device causes the wound-on member and the PWB to contact with each other with a contact force which is greater than a contact force produced by the weight of the PWB, and accordingly the PWB can be quickly conveyed at an acceleration and a deceleration which are greater than those employed in the conventional PWB conveyors.
(3) According to a third feature of the present invention that includes the second feature (2), the conveyor comprises two wound-on members, and four rotatable wheels on which the two wound-on members are wound to have respective straightly extending portions each of which straightly extends between corresponding two rotatable wheels of the four rotatable wheels and each of which contacts the printed wiring board, and the respective straightly extending portions of the two wound-on members extend parallel to each other in a first direction and are spaced from each other in a second direction, and the contact-force producing device biases one of the respective straightly extending portions of the two wound-on members, toward the other straightly extending portion. The present PWB conveyor includes two conveying units. Respective drive devices of the two conveying units may include a common drive source which is connected to respective drive rotatable wheels of the two conveying units that are mechanically coupled with each other. In this case, the two wound-on members are circulated at the same speed. Alternatively, the respective drive devices of the two conveying units may include respective exclusive drive sources which are so controlled as to rotate in synchronism with each other and thereby circulate the two wound-on members at the same speed. The PWB is conveyed while being sandwiched by the two wound-on members in a direction substantially parallel to the reference plane. In the case where the PWB is conveyed in a horizontal direction and it is assumed that the PWB is conveyed at an acceleration, xcex1, the PWB has a mass, m, and gravitational acceleration is g, the PWB receives a composite force, mxc2x7{square root over ( )}(g2xcex12), of the vertical-direction gravitational force, mxc2x7g, and the horizontal-direction inertia force, mxc2x7xcex1. On the other hand, if it is assumed that each conveying unit and the PWB contact each other with a contact force, F, and a friction coefficient is xcexc, a conveying force that can be applied to the PWB owing to the summed contact forces 2F is equal to 2 xcexcF. Therefore, if 2 xcexcF greater than mxc2x7{square root over ( )}(g2+xcex12), the PWB can be conveyed with the contact force F. In contrast, in the conventional PWB conveyor wherein a conveyor belt conveys a PWB while supporting a lower surface of the PWB, the frictional force produced between the PWB and the conveyor belt is equal to xcexcxc2x7mxc2x7g, and the maximum acceleration xcex1max at which the PWB is conveyed by the frictional force is equal to xcexcxc2x7g (i.e., xcex1max=xcexcxc2x7g). Therefore, if the contact force F that satisfies the condition that F greater than {mxc2x7gxc2x7{square root over ( )}(1+xcexc2)}/2xcexc is produced between the conveying units and the PWB, the PWB can be conveyed at an acceleration higher than that at which the PWB is conveyed by the conventional PWB conveyor. The present PWB conveyor can convey the PWB at a higher acceleration than the conventional PWB conveyor and can enjoy the above-described advantages of the PWB conveying method according to the first feature (1).
(4) According to a fourth feature of the present invention that includes the third feature (3), the contact-force producing device comprises at least one freely rotatable member which is rotatable about an axis line perpendicular to the first and second directions and which contacts one of opposite surfaces of the one straightly extending portion that is opposite to the other surface thereof at which the one straightly extending portion contacts the printed wiring board; and a biasing device which applies a biasing force to the freely rotatable member in a direction in which the one straightly extending portion is biased toward the other straightly extending portion. The freely rotatable member may be a roller or a ball. One or more rotatable wheels on which one wound-on member is wound may be used as one or more freely rotatable members. The position of the freely rotatable member in the direction of movement of the one wound-on member is not changeable, but the rotation of the freely rotatable member allows the movement of the one wound-on member. Thus, the freely rotatable member presses the one wound-on member against one side surface of the PWB, without interfering with the conveying of the PWB by the two wound-on members.
(5) According to a fifth feature of the present invention that includes the fourth feature (4), the contact-force producing device comprises a plurality of freely rotatable members, and a support member which supports the freely rotatable members along a straight line parallel to the one straightly extending portion, the biasing device being connected to the support member. The freely rotatable members press the one wound-on member against the one side surface of the PWB, since the biasing device biases the support member. Since the plurality of freely rotatable members press a plurality of portions of the straightly extending portion of the one wound-on member against the PWB, the two wound-on members can move the PWB straightly without tilting the same. In addition, since the biasing device biases the support member, the plurality of freely rotatable members are altogether pressed against the one wound-on member via the support member. Thus, the biasing device enjoys a simple construction.
(6) According to a sixth feature of the present invention that includes the fifth feature (5), the contact-force producing device further comprises a stopper which stops movement of the support member caused by the biasing force of the biasing device and thereby defines a limit of the movement of the support member. In the case where the present PWB conveyor employs the moving device according to the thirteenth feature (13), the stopper can accurately define the position of the one wound-on member which is in the state in which the one wound-on member is not in contact with the PWB and, owing to this effect, the distance by which the one wound-on member should be moved by the moving device can be decreased. In addition, even in the case where the moving device is not employed, the stopper contributes to easily providing the freely rotatable members supported by the support member, at respective positions where the freely rotatable members do not interfere with the conveying of the PWB caused by the two wound-on members into the space left between the two wound-on members. If the position of the stopper is adjustable, the above-indicated limit of movement of the support member is adjustable.
(7) According to a seventh feature of the present invention that includes the fourth feature (4), the contact-force producing device comprises a plurality of the freely rotatable members, a support member which supports the freely rotatable members along a straight line parallel to the one straightly extending portion, such that each of the freely rotatable members is movable in a direction perpendicular to the straight line, and a plurality of the biasing devices each of which is provided between the support member and a corresponding one of the freely rotatable members and biases the one freely rotatable member relative to the support member toward the one straightly extending portion. Since the plurality of freely rotatable members are individually pressed against the one wound-on member, each freely rotatable member can press the one wound-on member against the PWB with an appropriate pressing force even if the one side surface of the PWB is uneven.
(8) According to an eighth feature of the present invention that includes the seventh feature (7), the contact-force producing device further comprises a plurality of stoppers each of which stops movement relative to the support member of a corresponding one of the freely rotatable members caused by the biasing force of a corresponding one of the biasing devices and thereby defines a limit of the movement of the one freely rotatable member. The present PWB conveyor enjoys the same advantages as those of the PWB conveyor according to the sixth feature (6).
(9) According to a ninth feature of the present invention that includes any one of the fourth to eighth features (4) to (8), the biasing device comprises an elastic member which applies, as the biasing force, an elastic force to the freely rotatable member. The elastic member may be a spring such as a compression coil spring, or a member formed of rubber. The elastic force of the elastic member is so selected as to assure that owing to the contact force produced between the PWB and the two wound-on members, a frictional force greater than the gravitational force and the inertia force both of which are exerted to the PWB is obtained, as described previously. However, the elastic force or the contact force may be a prescribed constant value, or may be an adjustable value. In the latter case, the elastic force or the contact force may be adjusted depending on the shape, size, and weight of each PWB to be conveyed and/or a desired acceleration.
(10) According to a tenth feature of the present invention that includes the fourth or seventh feature (4) or (7), the biasing device comprises a pressurized-air-operated cylinder device which applies, as the biasing force, an operating force to the freely rotatable member. In this case, the contact force (or the pressing force) depends on the pressure in the air chamber of the pressurized-air-operated cylinder device. The air pressure may be a prescribed constant value, or may be a changeable or adjustable value. In the latter case, the air pressure may be changed or adjusted depending on the shape, size, and weight of each PWB to be conveyed and/or a desired acceleration.
(11) According to an eleventh feature of the present invention that includes any one of the third to tenth features (3) to (10), the conveyor further comprises a support device which supports the other straightly extending portion on one of opposite sides thereof that is opposite to the other side thereof on which the one straightly extending portion is provided. When the contact-force producing device biases the one wound-on member toward the other wound-on member, the support device supports the other wound-on member, so that the two wound-on members can stably contact the PWB and convey the same.
(12) According to a twelfth feature of the present invention that includes the eleventh feature (11), the support device comprises a support member which has a contact surface which contacts one of opposite surfaces of the other straightly extending portion that is opposite to the other surface thereof at which the other straightly extending portion contacts the printed wiring board. The other wound-on member slides on the contact surface of the support member. Accordingly, it is preferred that the contact surface have a low friction coefficient. For example, the contact surface is coated with a material, such as Teflon, which has a low friction coefficient, so that the contact surface has a low friction coefficient. Alternatively, the support member may be formed of Teflon. In addition, an inner surface of the other wound-on member that contacts the contact surface may be formed to have a low friction coefficient. The support member may be provided by one or more freely rotatable members.
(13) According to a thirteenth feature of the present invention that includes any one of the third to twelfth features (3) to (12), the conveyor further comprises a moving device which moves at least one of the two wound-on members toward, and away from, the other wound-one member. The moving device moves one wound-on member toward the other wound-on member, so that the two wound-on members sandwich and convey the PWB. The moving device moves one wound-on member away from the other wound-on member, so that the two wound-on members do not contact the side surfaces of the PWB.
(14) According to a fourteenth feature of the present invention that includes any one of the second to thirteenth features (2) to (13), the two rotatable wheels comprise two pulleys and the wound-on member comprises a belt.
(15) According to a fifteenth feature of the present invention that includes any one of the second to fourteenth features (2) to (14), the respective straightly extending portions of the two wound-on members as a first and a second wound-on member are spaced from each other in a substantially horizontal direction as the second direction, and the conveyor further comprises at least two third rotatable wheels in addition to the four rotatable wheels as two first rotatable wheels on which the first wound-on member is wound and two second rotatable wheels on which the second wound-on member is wound, at least one third wound-on member which is provided between the respective straightly extending portions of the first and second wound-on members and which is wound on the two third rotatable wheels to have a straightly extending portion which straightly extends parallel to the respective straightly extending portions of the first and second wound-on members, and a second drive device which is different from the drive device as a first drive device and which drives at least one of the third rotatable wheels. The PWB conveyor may employ one or more third conveying units each of which includes two third rotatable wheels, a third wound-on member wound on the third rotatable wheels, and a third drive device which drives at least one of the third rotatable wheels. The one or more third conveying units support the lower surface of the PWB and can convey the same at an acceleration not higher than a maximum acceleration depending on gravitational acceleration. Respective drive devices of the first and second conveying units which horizontally sandwich the PWB and the one or more third conveying units which support the lower surface of the PWB, may employ a common drive source, or respective exclusive drive sources. The third conveying unit may be used to carry in the PWB to the first and second conveying units, or carry out the PWB from the latter conveying units, or may be used to just support, when the first and second conveying units horizontally sandwich the PWB, the lower surface of the PWB and thereby help the latter conveying units easily sandwich the PWB. In the former case, for example, the supplying of a PWB to the present PWB conveyor can be easily performed by a PWB conveyor of a type which conveys the PWB while supporting the lower surface thereof. When the first and second conveying units convey the PWB while sandwiching the PWB, the wound-on member of the third conveying unit may be kept spaced from the PWB, or may be kept in contact with the PWB. In the latter case, the wound-on member of the third conveying unit may be moved in synchronism with the respective wound-on members of the first and second conveying units, or may be kept stopped. When the third conveying unit conveys the PWB, the respective wound-on members of the first and second conveying units are kept spaced away from each other. During this operation, the respective wound-on members of the first and second conveying units may be moved in synchronism with each other, or may be kept stopped, so as to function as two guide members which guide the movement of the PWB.
(16) According to a sixteenth feature of the present invention that includes the fifteenth feature (15), the conveyor comprises two third wound-on members which correspond to the first and second wound-on members, respectively, and four third rotatable wheels on which the two third wound-on members are wound, two of which correspond to the two first rotatable wheels, and the other two of which correspond to the two second rotatable wheels. In the case where the present PWB conveyor employs a single third conveying unit, it is preferred that the third wound-on member and the third rotatable wheels have a great width in a widthwise direction of the PWB, i.e., a direction perpendicular to the PWB-convey direction, so that the third wound-on member supports at least the lower surface of a widthwise middle portion of the PWB. In this case, however, a space under the PWB is occupied by the elements of the third conveying unit. In contrast, the present PWB conveyor employs two third conveying units. If the two third conveying units are provided at respective positions distant from each other in the widthwise direction of the PWB, a free space can be obtained under the PWB.
(17) According to a seventeenth feature of the present invention that includes the second feature (2), the straightly extending portion of the wound-on member extends in a substantially horizontal direction, and the contact-force producing device comprises at least one freely rotatable member which is provided above the straightly extending portion of the wound-on member such that the freely rotatable member is freely rotatable about a substantially horizontal axis line perpendicular to the substantially horizontal direction, and which contacts an upper surface of the printed wiring board whose lower surface is supported on the straightly extending portion; and a biasing device which biases the freely rotatable member toward the upper surface of the printed wiring board. The contact-force producing device may be one which produces respective contact forces on both of widthwise opposite ends of the PWB as seen in the widthwise direction thereof, or one which produces a contact force on only one of the widthwise opposite ends of the PWB. According to the seventeenth feature (17), the PWB is pressed against the wound-on member owing to both the weight of the PWB and the biasing force of the biasing device. Thus, the contact force produced between the PWB and the wound-on member is naturally greater than the weight of the PWB, and accordingly the wound-on member can quickly move the PWB at an acceleration higher than a maximum acceleration depending upon gravitational acceleration. The present PWB conveyor may employ any one of the fifth to twelfth and fourteenth features (5) to (12) and (14).
(18) According to an eighteenth feature of the present invention that includes the seventeenth feature (17), the conveyor further comprises a moving device which moves the freely rotatable member toward, and away from, the straightly extending portion of the wound-on member. When the PWB is carried in onto the wound-on member, the freely rotatable member is moved away from the wound-on member and, after the carrying-in of the PWB, the freely rotatable member is moved toward the wound-on member to press the PWB against the wound-on member.